Diodes include vacuum tube diodes and semiconductor diodes. The semiconductor diodes include a point-contact diode, a junction diode, a tunnel diode, a photo-diode, and a varactor diode.
A varactor diode is a variable reactor diode, and the capacitance thereof changes according to the applied voltage. (Hereinafter, the term “varactor” will be used to refer to a varactor diode or a variable capacitor.)
According to a related technology, an N+/P well junction varactor has been manufactured using a CMOS process. However, if a large capacitance (Cjo) is required in the related N+/P well varactor, the size of a corresponding N+ area must be increased. Accordingly, the size of the element must be enlarged.